The present invention relates to tubular casings based on cellulose hydrate which carry on their inside surface a coating of a mixture of chemically modified starch and natural oils which can be easily peeled off from the filling mass. Furthermore, the present invention relates to a process for the manufacture of such tubular casings. Finally, the present invention relates to the use of such tubular casings as a packaging material, in particular as an artificial sausage casing which can be easily removed from the sausage mass.
Tubular cellulose hydrate casings, the inside of which is not pre-treated, have only a limited suitability for use as sausage casings, because, in the case of fresh sausage, the sausage mass adheres so firmly to the casing that it is almost impossible to separate the casing from the sausage mass when required. In the case of long-keeping or summer sausages, on the other hand, the adhesion is so slight that the casing already detaches itself from the sausage mass during the drying step when the sausage is prepared. Because it detaches itself from the sausage mass when the summer sausage is dried, the casing does not shrink together with the sausage mass and thus becomes crumpled and unsightly, and such properties impede the sales of the sausage.
It has already been suggested to avoid these drawbacks by providing the inside of cellulose hydrate based casings with a layer comprising chemical compounds which act as release agents, such as long-chain isocyanates, ethylene imines, chromium fatty acid complexes, silicones, perfluorinated chemical compounds, diketenes and the like.
Furthermore, artificial sausage casings for long-keeping sausages based on cellulose hydrate are known which carry on their inside surface a layer comprising albuminous chemical compounds, in order to create a satisfactory adhesion between the sausage mass and the sausage casing. Such albuminous compounds are, e.g., chemically modified proteins, epichlorhydrin/polyamine polyamide resins, urea- or melamine-formaldehyde resins, and the like.
These finishing processes for treating the inside surfaces of artifical sausage casings based on cellulose hydrate have the drawback, however, that they are very expensive, because in most cases specific manufacturing conditions must be maintained for the chemical reaction between the cellulose hydrate and the chemical compounds from which the coating is formed. Furthermore, the known finishing processes invariably require the use of chemical compounds of complicated chemical structure which are relatively expensive.
Frequently, such treatments involve the risk that the cellulose hydrate forming the tubular casing is cross-linked in an undesirable and uncontrollable manner by the use of the above-mentioned chemical compounds, so that the sausage casing becomes brittle and breaks. Thus, holes may appear in the wall of the sausage casing when the casing is used in accordance with its purpose, e.g., shirred into a stick.